1. Technical Field
The present invention relates generally to an improved circuit topology for providing an array of individually tuned oscillators. More specifically, the present invention provides an oscillator array with row and column control that provides a plurality of individually tuned oscillators operating at different frequencies.
2. Description of Related Art
Random numbers are used in various encryption applications, which are particularly important in providing security for e-commerce applications as well as for a wide variety of other computer based or internet based communications and transactions. One approach to generating random numbers uses ring oscillators. In one approach using ring oscillators, a free running ring oscillator is used to clock a linear feedback shift register (LFSR). In another random number generator a single, slow voltage controller oscillator (VCO), which receives a noise input, samples the output of high speed ring oscillators.
One problem with some ring oscillator based random number generators, is that the sample frequency may be correlated to the ring oscillator frequency for a duration long enough to cause individual random number generator bits to be correlated and therefore, less random. It would be desirable to provide a random number generator that reduces or eliminates that correlation and produces random numbers that are more unpredictably random.
In U.S. Pat. No. 6,480,072 issued to Walsh et al. on Nov. 12, 2002, which is hereby incorporated by reference, this problem was addressed by utilizing an oscillator in an open loop configuration, such as a voltage controlled oscillator (VCO), whose output frequency is randomly controlled. The VCO output signal is sampled at a frequency much lower than, and asynchronous to, the frequency of the VCO output signal. The frequency of the VCO output signal is made to change significantly during each sample period. Due to the asynchronous relationship between the VCO output signal and the sample clock and the significant change in frequency during the sampling period, the exact number of VCO output periods, including any fractional parts, varies during each sample period. That variation is the basis for creating unpredictable randomness.
In U.S. Pat. No. 5,706,218 issued to Eric Hoffman on Jan. 6, 1998, which is hereby incorporated by reference, a random number generator is disclosed that uses a plurality of high frequency ring oscillators and a single, slow, voltage controlled oscillator which receives a noise input. The ring oscillators are sampled under control of the slow oscillator. A circuit is used between the output of each of the ring oscillators and its respective D-type latch to assure that the sampling is unbiased, that is, that there will be near even distribution of 1s and 0s in the random numbers.
Other random number generator mechanisms are described in, for example, U.S. Pat. Nos. 6,667,665; 4,905,176; 5,117,380; 5,963,104; and 6,480,870. In some of these random number generator mechanisms, the random number generator is not a true random number generator but rather a pseudo-random number generator. In many of these random number generators, negative affects of injection locking, large chip area requirements, and large amounts of design and layout time are experienced. It would be beneficial to have an improved mechanism for generating truly random numbers, as opposed to pseudo-random numbers, that results in minimal injection locking, minimal chip area requirements, and minimal amounts of design and layout time.